Varia RearVue 820 combines a bicycle tail light with radar that tracks traffic behind the rider. It can detect approaching vehicles from more than 170 metres away, with alerts shown on a compatible Edge cycling computer or in the Varia phone app.
Rather than reporting only that something is approaching, the system shows a vehicle-size category, lateral movement between lanes and an assessed threat level. It can also track a vehicle travelling at roughly the cyclist’s speed for a time. The tail light changes its flash pattern when the rider slows or stops.
The alerts can improve awareness of traffic behind, but the rider still needs to check the road before a manoeuvre. Same-speed tracking may be limited at low speeds, in heavy rain or snow, or when the radar’s view of the road is obstructed. Mounting and riding conditions therefore affect what the device can report.